1. Field of the Invention
The present invention relates to mechanical character recognition apparatus, and more particularly to such apparatus incorporating an optical wand for scanning characters to be recognized and for producing a scan pattern in response thereto.
2. The Prior Art
U.S. Pat. No. 3,947,817 discloses an optical wand, which is adapted to be manually moved in an arbitrary direction relative to a row of characters, at a given maximum speed, for generating signals corresponding to the features of the characters. Such wands are used as peripheral data acquisition systems and have wide application in connection with POS terminals for reading labels; bank terminals for reading account numbers on checks and documents; and other terminals such as those for reading identity cards, etc. The signals produced by the wand pose a relatively difficult character recognition problem, on account of the variations in the manual scanning process.
Such wands must be easy to handle and must be functionally reliable. Reliability has proved difficult to achieve, because the manual scanning of the characters produces a relatively wide variation of scanning conditions. For example, the paper or other carrier on which the characters appear may have considerably different reflection properties from time to time; the manual scanning process is carried out at different times at different speeds, with reversal of the scanning direction; and during the scanning, the wand may be tilted or even moved obliquely relative to the row of characters. Despite these difficulties, it is important that characters be scanned once and only once, and not omitted, because duplicate scanning or omission leads to faulty information.
The price-efficiency ratio of the wand is also important, since wands can be economically employed in connection with data acquisition systems only if they are adaptable to various applications, so that a flexible basic device may be manufactured in large numbers, and readily modified for several applications.
In the prior art, the various conditions imposed on such wands have led to a compromise, which limit their capacities. In particular, the classification methods which have been used are limited to relatively simple ones, which permit easy character recognition of single characters during the time allowed by the scanning speed. This not only limits the application of the wand to a specific type of character, but also to a relatively small number of characters. Even so, the recognition reliability is not great so that frequently the characters are not recognized and must be rescanned before recognition is possible.
It is also known in the prior art to carry out a plurality of recognition steps upon the scanned characters as they are being scanned, i.e., to make available and analyze instantaneous scan patterns which occur during scanning.
In the aforementioned U.S. patent, the scanning output from a photo diode matrix is used to form row codes. A character code is then derived from the row codes and, from a sequence of row codes, the most significant row code is selected in order to deduce the class association. This technique is effective only with character sections in specific preselected fields of vision of the diode matrix and blanks between those character sections. As the classification of characters is based on the analyzing effect of combinations of simple features, it is fundamentally impossible to exceed relatively low limits of recognition reliability.
More elaborate classification methods which are typically used in connection with high-speed document printers such as described in German Pat. No. 2,619,014, but such methods require relatively large intervals of time to reliably classify characters, and are therefore not suitable for use with hand manipulated scanners.